Not applicable.
Not applicable.
The present invention relates generally to portable computers and particularly to battery operated portable computers. More particularly, the present invention relates to portable computers that detect when a battery gauge is out of calibration.
Effective battery design has been at the forefront of computer system development in recent years. Batteries store an electric charge, which is gradually released to power the computer circuitry. Laptop computers in particular are designed to operate on battery power, allowing the computer to be used in virtually any location. One drawback to running a computer on battery power is that the user is limited to a finite number of hours of computing time before the battery capacity is depleted. Thus, maximizing battery life is desirable. The exact amount of operating time that a battery provides depends on a number of factors, including the charge storage capacity of the battery, the operating speed of the computer, and the number of transistors in the computer. Higher operating speeds and more transistors, which generally permit higher performance, generally draw more power. Thus, power requirements continue to increase as computer manufacturers strive to improve performance, increasing the demand for higher battery capacity.
Manufacturers have employed a variety of techniques to extend battery operating time, including modifications to computer hardware, special power-saving software algorithms, and improvements in battery technology. Many computer components, especially in laptop computers, are designed to shut down after a period of inactivity, even while the rest of the computer continues to operate. The display screen, for example, may darken or turn off if the user fails to type on the keyboard or move the mouse after a predetermined period of time. Similarly, the disk drive may shut off if not accessed for a period of time. Many computer systems are capable of entering a special xe2x80x9csleepxe2x80x9d mode in which virtually the entire computer shuts down, including the central processing unit (CPU), although the memory contents are retained so that the computer can return to normal operation within a few seconds. Older computers relied on instructions stored in the computer hardware known as the Advanced Power Management (APM) to determine when to shut down selected components. Newer computer designs which conform to the Advanced Configuration and Power Interface (ACPI) standard, developed by Intel, Microsoft, and Toshiba, rely on the operating system (e.g., Windows 98) software to turn individual components on and off. Power control, through either hardware or software, extends the battery life by drawing power only as needed.
Recent improvements in battery design have extended battery life, as well. Previously, battery voltage would decrease as the charge drained, eventually dropping off very quickly as the capacity neared zero. Although some electric charge would remain, these batteries could not regain the required operating voltage without being recharged. Newer batteries, by contrast, tend to have a more linear discharge curve. When the battery output voltage drops below the desired operating voltage, modem computers typically have about four to eight seconds of operation time left before no power remains, terminating computer operation. Thus, modem batteries last longer by operating more efficiently.
In order to prevent the computer from suddenly shutting down due to a drained battery, possibly resulting in data loss, computer software continuously tracks the battery level and notifies the user of the remaining battery power. Some computers, upon nearing complete discharge, prevent data loss by automatically saving the memory contents to disk and then shutting the computer down. The user then must recharge the battery, insert another computer battery, or plug the computer into a wall socket to resume computing.
Accordingly, it is desirable to know how much battery charge remains when operating on battery power. Typically, the amount of remaining charge is determined by continuously measuring battery output current, beginning after the battery is recharged. Because the exact capacity of charge a battery can store is affected by many parameters, include age, temperature, etc., the battery monitor assumes the battery charged to a xe2x80x9clast known capacityxe2x80x9d of the battery pack. The remaining battery level then is determined by subtracting the spent charge from the last known battery capacity.
Because of the nature of battery chemistry, however, accurately determining the amount of charge stored in the battery after recharging can prove difficult. Some rechargeable batteries exhibit a phenomenon known as the xe2x80x9cmemory effect,xe2x80x9d in which the battery cannot charge to full capacity unless first being completely discharged. If a battery is discharged to 90% of its initial charge level and then recharged, for example, then recharging the battery will not succeed in filling the battery to 100% of its charge capacity. Instead, the battery will stop recharging before reaching full capacity. Repeated charge/discharge cycles enhance the memory effect, causing the battery to reach successively lower levels of charge after each recharge. Whenever the memory effect prevents the battery from charging to capacity, the battery gauge reflects a higher level of charge than the battery actually stores because the calculated value is based on the last known battery capacity. The memory effect thus can reduce the accuracy of a battery gauge by increasing the difference between the last known battery capacity and the actual charge level after recharging. Accordingly, the battery gauge may indicate that there is charge remaining when the battery reaches complete discharge. Also, the last known capacity cannot account for temperature variations, load conditions or self discharging of the battery.
To compensate for the battery gauge inaccuracy, the computer systems in the past have saved memory shut down when the charge level falls below a predetermined cutoff point. The cutoff point, which typically represents a percentage of the total battery capacity, is set sufficiently high to prevent unexpected loss of power. Though effective in preventing unexpected shut down, this early shut down technique reduces the amount of operating time for the user. In addition, because the battery never reaches complete discharge, the memory effect, if any, circumvents accurate measurement of the charge level by preventing the battery from fully recharging again.
For the foregoing reasons, it would be desirable to have a computer system capable of monitoring battery gauge calibration and alerting the user that a battery calibration is required. Such a computer system would greatly enhance computer functionality.
Accordingly, the present invention discloses a computer system with a rechargeable battery which is capable of monitoring the calculated capacity calibration of the battery gauge to determine whether the calibration corresponds to the actual battery capacity. More specifically, the computer system monitors a battery capacity register in battery logic associated with the system battery when the battery is nearing a full charge, and when the battery is on the verge of being depleted. During a charge cycle of the battery, the computer system monitors the battery capacity register. If the battery capacity register reaches a maximum capacity indication more than ten minutes before the battery actually reaches a valid charge termination, this indicates the battery capacity register is out of calibration. A valid charge termination is determined by a keyboard controller monitoring system battery voltage for a drop in overall voltage which characteristically indicates that the battery capacity has been charged to a maximum amount. Likewise, if the system battery reaches a valid charge termination and the battery capacity register shows less than ninety percent charge capacity, the battery gauge is too far out of calibration. During computer system operation on the system battery, the keyboard controller monitors the battery capacity register in relation to the low battery signal. If the battery capacity register reaches a zero percent indication more than ten minutes before assertion of the depleted battery signal, the battery capacity register is too far out of calibration or depleted. Likewise, if the battery capacity register indicates ten percent indication when the low or depleted battery signal is asserted by the keyboard controller, the battery capacity register is too far out of calibration.
In all of these instances where the battery register exceeds calibration tolerance, the keyboard controller notifies system software so that the bezel software can notify the user to run a battery system calibration. This notification comprises sending a unique scan code, much like the scan codes sent when a user presses a key on the keyboard. Upon receiving this scan code that uniquely identifies that the battery capacity register is out of calibration, the system software notifies the user in some appropriate way.